The invention relates to a device for regulating the traveling speed of a motor vehicle by means of an electric speed regulator which compares the prevailing actual speed with a desired rated or selected speed and in the case of a deviation therebetween transmits a signal dependent on the magnitude of the deviation to a correcting element which controls the fuel air mixture supplied to the vehicle engine, by means which produce a delayed change of the signal transmitted to the correcting element upon a change of the rated speed.
Known devices of this kind are designed to effect an automatic regulation of the traveling speed when the automatic operation is switched on, so that upon the occurrence of variables, such as load variations caused, for example, by variations in the grade or inclination of the street or road variations in the traveling speed will not occur. However, it is desirable that at the switching of the device from the normal operation of the motor vehicle to automatic regulation of the traveling speed, if possible no decrease in the speed during the transition from the driver-regulated to the automatically regulated speed occurs. In this case, the device is to present a very rapid adjustment. On the other hand, however, abrupt changes in the traveling speed are to be avoided when during the automatic regulation of the traveling speed, the rated or set speed is modified, since without means for producing a delayed change of the signal transmitted to the correcting element upon a modification or increase of the set speed, the correcting element is first brought into the full-throttle position and only thereafter returned to the position required for maintaining the rated speed.
In order to avoid the unsatisfactory mode of operation last described and to permit a smooth transition when the set speed is modified, while upon the occurrence of load variations only small deviations occur, it has been proposed that, as means for producing a delayed change of the signal transmitted to the correcting element upon a modification, of the set speed, a stage be provided between the regulator and the correcting element which transmits each signal change up to a prespecified amplitude value without delay, and above this amplitude value, transmits the signal with delay to the correcting element or a control stage that controls the correcting element. Thereby, the signal acting upon the control stage is transformed in such a way that at each deviation the control stage starts removing the deviation at great adjustment speed and, after a first partial elimination, terminates the regulating process with a smaller adjustment speed. Thereby, a yerk-free regulation at modifications in the rated speed is achieved. The operation of this known device, however, is still imperfect, since the prespecified amplitude value of the delay means to accomplish a signal modification must be determined as a compromise for all occurring states of operation. Therefore, the device cannot neutralize the speed changes for all possible load variations as quickly as possible.